The present invention relates to a lighting device for an observation device and to an observation device.
For example, an observation device may involve an operating microscope. In particular, the observation device can be designed as an ophthalmologic operating microscope, which is utilized, for example, for a special application in eye surgery, i.e., cataract surgery.
In the case of cataract surgery, a lens of the eye—which is clouded, for example, due to the cataract—is replaced by an artificial lens.
The lens of an eye is found inside a thin envelope, the so-called lens capsule. In order to remove the lens, access to it is created to it by a thin cut made in the lens capsule and the lens is next broken up into small pieces with a microsurgical instrument, and then these pieces are removed by means of an aspirating device.
This process takes place under microscopic observation—for example, under stereomicroscopic observation—employing a specially designed lighting device for such interventions. This lighting device presents both an illumination of the surrounding field, which is necessary for illuminating the entire operating field, as well as a red background illumination for the actual operating field limited to the pupil region of the lens, which is of decisive importance for the cataract operation. This red background illumination is derived from that fraction of illuminating light, which, after passing through the transparent media of the eye, finally strikes the retina, which appears red due to good blood perfusion, is back-scattered therefrom, and then can also be observed, of course, as an apparent red background illumination, by the surgeon by means of the operating microscope. This very characteristic red background illumination in cataract surgery is generally known in professional circles under the term “red reflex”.
For an optimal recognition of details relevant for the cataract operation, a red background illumination that is as homogeneous as possible has proven to be a necessary prerequisite for the surgeon. A first requirement of the lighting device is thus to assure a homogeneity of the red reflex that is as good as possible over the entire pupil of the patient.
For complete elimination of the lens pieces of the lens of the eye which has been broken up into tiny pieces and for good recognition of transparent membranes, for example, the lens capsule, another requirement must be fulfilled, that is, a good contrasting of phase objects and in fact, this contrast should also be provided as much as possible over the entire pupil of the patient.
In the past, various solutions have already been made known in connection with the production of such red background illumination.
In U.S. Pat. No. 4,779,968 a coaxial illumination for an operating microscope is described.
According to this solution, a lighting module is provided, which can be advantageously incorporated as an additional module in existing operating microscopes. This additional module is preferably introduced on the object side underneath the principal objective of the observation device. The illumination is coupled to the axis of the microscope either with a separating plate or a separating cube.
A lighting device for an operating microscope is described in DE 4,028,605 C2, which permits a combination of zero-degree, coaxial and oblique illumination. For this purpose, the lighting device makes available movable mirror sections as well as a stationary six-degree mirror plus the respective variable diaphragms, by which means the angle of illumination and the light components of the respective lighting device can be varied. The key point of this known solution lies in the increase in contrast by means of a coaxial illumination, wherein the coaxial lighting involves an oblique illumination in the vicinity of the axis.
An ophthalmologic observation device is disclosed in DE 196 38,263 A1, in which the unavoidable corneal reflex that occurs when a patient's eye is illuminated for observation of the front segments of the eye will be suppressed. This is done by introducing a light absorber in the form of a black point in the vicinity of a luminous-field diaphragm of an otherwise known illumination.
A switchable lighting system for an ophthalmologic operating microscope is described in U.S. Pat. No. 6,011,647, in which the system can be switched between a surrounding field lighting and an optimized “red reflex” illumination during the operation. The lighting device is comprised of a light source, a collector, a luminous-field diaphragm, a tilting mirror, a field lens and a principal objective. In the case of this optimized “red reflex” lighting, the helix of the light source is then imaged or mapped in the pupil of the eye as the object plane and not the luminous-field diaphragm, as is the case with surrounding field lighting.
In EP 1,109,046 A1, finally, a lighting device is disclosed for an operating microscope, which has two reflection elements which can be moved independent of one another, by means of which both the angle of the incident light can be changed relative to the optical axis of the microscope objective and the intensity of the different light beams can be varied, independent of one another.
In the chronological sequence of the proposed solutions known from the prior art, first a “red reflex” illumination is favored under exactly zero degrees. The advantage of such a zero-degree lighting or a true coaxial lighting, respectively, lies in the production of a good homogeneity of the red reflex. The second fundamental requirement also described above of a good contrasting of the lens pieces in the lens capsule and the presentation of the capsule membrane is not sufficiently fulfilled, however, by the known lighting systems with zero-degree illumination.
A next step in the development then led to lighting in the vicinity of the axis (also referred to as coaxial illumination), in order to obtain an improvement of the contrasting. Due to the angle which varies in magnitude between the observation axis and the lighting axis, however, a shading of the red reflex that is of variable intensity is obtained, thus the disadvantage of an inhomogeneity of the red reflex. Lastly, coaxial lighting represents a compromise solution between oblique lighting and zero-degree lighting. As a consequence, the advantage of an improved contrasting leads to a deterioration in homogeneity.
The proposed solutions known from the prior art all have the disadvantage that the requirements relative to homogeneity and contrasting cannot be fulfilled simultaneously as a consequence of the inconsistencies that necessarily occur.